Connected: An Internet Encyclopedia
RFC 1812 - 5.2.1.1 General

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### 5.2.1.1 General

This section covers the general forwarding algorithm. This algorithm applies to all forms of packets to be forwarded: unicast, multicast, and broadcast.

1. The router receives the IP packet (plus additional information about it, as described in Section [3.1]) from the Link Layer.

2. The router validates the IP header, as described in Section [5.2.2]. Note that IP reassembly is not done, except on IP fragments to be queued for local delivery in step (4).

3. The router performs most of the processing of any IP options. As described in Section [5.2.4], some IP options require additional processing after the routing decision has been made.

4. The router examines the destination IP address of the IP datagram, as described in Section [5.2.3], to determine how it should continue to process the IP datagram. There are three possibilities:

   - The IP datagram is destined for the router, and should be queued for local delivery, doing reassembly if needed.

   - The IP datagram is not destined for the router, and should be queued for forwarding.

   - The IP datagram should be queued for forwarding, but (a copy) must also be queued for local delivery.

Next: 5.2.1.2 Unicast

Connected: An Internet Encyclopedia
RFC 1812 - 5.2.1.1 General